Network Working Group P. Rzewski
Request for Comments: 3570 Media Publisher, Inc.
Category: Informational M. Day
Cisco
D. Gilletti
July 2003
Content Internetworking (CDI) Scenarios
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
In describing content internetworking as a technology targeted for
use in production networks, it is useful to provide examples of the
sequence of events that may occur when two content networks decide to
interconnect. The scenarios presented here seek to provide some
concrete examples of what content internetworking is, and also to
provide a basis for evaluating content internetworking proposals.
Table of Contents
1. Introduction...................................................21.1. Terminology..............................................32. Special Cases of Content Networks..............................32.1. Publishing Content Network...............................32.2. Brokering Content Network................................32.3. Local Request-Routing Content Network....................43. Content Internetworking Arrangements...........................54. Content Internetworking Scenarios..............................54.1. General Content Internetworking..........................6
4.2. BCN providing ACCOUNTING INTERNETWORKING and
REQUEST-ROUTING INTERNETWORKING..........................94.3. BCN providing ACCOUNTING INTERNETWORKING................114.4. PCN ENLISTS multiple CNs................................124.5. Multiple CNs ENLIST LCN.................................135. Security Considerations.......................................155.1. Threats to Content Internetworking......................155.1.1. Threats to the CLIENT.............................15Rzewski, et al. Informational [Page 1]

RFC 3570 CDI Scenarios July 20035.1.2. Threats to the PUBLISHER..........................175.1.3. Threats to a CN...................................176. Acknowledgements..............................................187. References....................................................188. Authors' Addresses............................................199. Full Copyright Statement......................................201. Introduction
In [1], the concept of a "content network" is introduced and
described. In addition to describing some general types of content
networks, it also describes motivations for allowing content networks
to interconnect (defined as "content internetworking").
In describing content internetworking as a technology targeted for
use in production networks, it's useful to provide examples of the
sequence of events that may occur when two content networks decide to
interconnect. Naturally, different types of content networks may be
created due to different business motivations, and so many
combinations are likely.
This document first provides detailed examples of special cases of
content networks that are specifically designed to participate in
content internetworking (Section 2). We then discuss the steps that
would be taken in order to "bring up" or "tear down" a content
internetworking arrangement (Section 3). Next we provide some
detailed examples of how content networks (such as those from Section2) could interconnect (Section 4). Finally, we describe any security
considerations that arise specifically from the examples presented
here (Section 5).
The scenarios presented here answer two distinct needs:
1. To provide some concrete examples of what content internetworking
is, and
2. To provide a basis for evaluating content internetworking
proposals.
A number of content internetworking systems have been implemented,
but there are few published descriptions. One such description is
[2].
1.1. Terminology
Terms in ALL CAPS are defined in [1] except for the following terms
defined below in this document: PCN, BCN, and LCN. Additionally, the
term SLA is used as an abbreviation for Service Level Agreement.
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RFC 3570 CDI Scenarios July 20032. Special Cases of Content Networks
A CN may have REQUEST-ROUTING, DISTRIBUTION, and ACCOUNTING
interfaces. However, some participating networks may gravitate
toward particular subsets of the CONTENT INTERNETWORKING interfaces.
Others may be seen differently in terms of how they relate to their
CLIENT bases. This section describes these refined cases of the
general CN case so they may be available for easier reference in the
further development of CONTENT INTERNETWORKING scenarios. The
special cases described are the Publishing Content Network, the
Brokering Content Network, and the Local Request-Routing Content
Network.
2.1. Publishing Content Network
A Publishing Content Network (PCN), maintained by a PUBLISHER,
contains an ORIGIN and has a NEGOTIATED RELATIONSHIP with two or more
CNs. A PCN may contain SURROGATES for the benefit of serving some
CONTENT REQUESTS locally, but does not intend to allow its SURROGATES
to serve CONTENT on behalf of other PUBLISHERS.
Several implications follow from knowing that a particular CN is a
PCN. First, the PCN contains the AUTHORITATIVE REQUEST-ROUTING
SYSTEM for the PUBLISHER's CONTENT. This arrangement allows the
PUBLISHER to determine the distribution of CONTENT REQUESTS among
ENLISTED CNs. Second, it implies that the PCN need only participate
in a subset of CONTENT INTERNETWORKING. For example, a PCN's
DISTRIBUTION INTERNETWORKING SYSTEM need only be able to receive
DISTRIBUTION ADVERTISEMENTS, it need not send them. Similarly, a
PCN's REQUEST-ROUTING INTERNETWORKING SYSTEM has no reason to send
AREA ADVERTISEMENTS. Finally, a PCN's ACCOUNTING INTERNETWORKING
SYSTEM need only be able to receive ACCOUNTING data, it need not send
it.
2.2. Brokering Content Network
A Brokering Content Network (BCN) is a network that does not operate
its own SURROGATES. Instead, a BCN operates only CIGs as a service
on behalf other CNs. A BCN may therefore be regarded as a
"clearinghouse" for CONTENT INTERNETWORKING information.
For example, a BCN may choose to participate in DISTRIBUTION
INTERNETWORKING and/or REQUEST-ROUTING INTERNETWORKING in order to
aggregate ADVERTISEMENTS from one set of CNs into a single update
stream for the benefit of other CNs. To name a single specific
example, a BCN could aggregate CONTENT SIGNALS from CNs that
represent PUBLISHERS into a single update stream for the benefit of
CNs that contain SURROGATES. A BCN may also choose to participate in
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RFC 3570 CDI Scenarios July 2003
ACCOUNTING INTERNETWORKING in order to aggregate utilization data
from several CNs into combined reports for CNs that represent
PUBLISHERS.
This definition of a BCN implies that a BCN's CIGs would implement
the sending and/or receiving of any combination of ADVERTISEMENTS and
ACCOUNTING data as is necessary to provide desired services to other
CONTENT NETWORKS. For example, if a BCN is only interested in
aggregating ACCOUNTING data on behalf of other CNs, it would only
need to have an ACCOUNTING INTERNETWORKING interface on its CIGs.
2.3. Local Request-Routing Content Network
Another type of CN is the Local Request-Routing CONTENT NETWORK
(LCN). An LCN is defined as a type of network where CLIENTS' CONTENT
REQUESTS are always handled by some local SERVER (such as a caching
proxy [1]). In this context, "local" is taken to mean that both the
CLIENT and SERVER are within the same administrative domain, and
there is an administrative motivation for forcing the local mapping.
This type of arrangement is common in enterprises where all CONTENT
REQUESTS must be directed through a local SERVER for access control
purposes.
As implied by the name, the LCN creates an exception to the rule that
there is a single AUTHORITATIVE REQUEST-ROUTING SYSTEM for a
particular item of CONTENT. By directing CONTENT REQUESTS through
the local SERVER, CONTENT RESPONSES may be given to CLIENTS without
first referring to the AUTHORITATIVE REQUEST-ROUTING SYSTEM. Knowing
this to be true, other CNs may seek a NEGOTIATED RELATIONSHIP with an
LCN in order to perform DISTRIBUTION into the LCN and receive
ACCOUNTING data from it. Note that once SERVERS participate in
DISTRIBUTION INTERNETWORKING and ACCOUNTING INTERNETWORKING, they
effectively take on the role of SURROGATES. However, an LCN would
not intend to allow its SURROGATES to be accessed by non-local
CLIENTS.
This set of assumptions implies multiple things about the LCN's
CONTENT INTERNETWORKING relationships. First, it is implied that the
LCN's DISTRIBUTION INTERNETWORKING SYSTEM need only be able to send
DISTRIBUTION ADVERTISEMENTS, it need not receive them. Second, it is
implied that an LCN's ACCOUNTING INTERNETWORKING SYSTEM need only be
able to send ACCOUNTING data, it need not receive it. Finally, due
to the locally defined REQUEST-ROUTING, the LCN would not participate
in REQUEST-ROUTING INTERNETWORKING.
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RFC 3570 CDI Scenarios July 20033. Content Internetworking Arrangements
When the controlling interests of two CNs decide to interconnect
their respective networks (such as for business reasons), it is
expected that multiple steps would need to occur.
The first step would be the creation of a NEGOTIATED RELATIONSHIP.
This relationship would most likely take the form of a legal document
that describes the services to be provided, cost of services, SLAs,
and other stipulations. For example, if an ORIGINATING CN wished to
leverage another CN's reach into a particular country, this would be
laid out in the NEGOTIATED RELATIONSHIP.
The next step would be to configure CONTENT INTERNETWORKING protocols
on the CIGs of the respective CNs in order to technically support the
terms of the NEGOTIATED RELATIONSHIP. To follow our previous
example, this could include the configuration of the ENLISTED CN's
CIGs in a particular country to send DISTRIBUTION ADVERTISEMENTS to
the CIGs of the ORIGINATING CN. In order to configure these
protocols, technical details (such as CIG addresses/hostnames and
authentication information) would be exchanged by administrators of
the respective CNs.
Note also that some terms of the NEGOTIATED RELATIONSHIP would be
upheld through means outside the scope of CDI protocols. These could
include non-technical terms (such as financial settlement) or other
technical terms (such as SLAs).
In the event that the controlling interests of two CNs no longer wish
to have their networks interconnected, it is expected that these
tasks would be undone. That is, the protocol configurations would be
changed to cease the movement of ADVERTISEMENTS and/or ACCOUNTING
data between the networks, and the NEGOTIATED RELATIONSHIP would be
legally terminated.
4. Content Internetworking Scenarios
This section provides several scenarios that may arise in CONTENT
INTERNETWORKING implementations.
Note that we obviously cannot examine every single permutation.
Specifically, it should be noted that:
o Any one of the interconnected CNs may have other CONTENT
INTERNETWORKING arrangements that may or may not be transitive to
the relationships being described in the diagram.
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RFC 3570 CDI Scenarios July 2003
o The graphical figures do not illustrate the CONTENT REQUEST paths.
It is assumed that a REQUEST-ROUTING SYSTEM eventually returns to
the CLIENT the IP address of the SURROGATE deemed appropriate to
honor the CLIENT's CONTENT REQUEST.
The scenarios described include a general case, two cases in which
BCNs provide limited interfaces, a case in which a PCN enlists the
services of multiple CNs, and a case in which multiple CNs enlist the
services of an LCN.
4.1. General Content Internetworking
This scenario considers the general case where two or more existing
CNs wish to establish a CONTENT INTERNETWORKING relationship in order
to provide increased scale and reach for their existing customers.
It assumes that all of these CNs already provide REQUEST-ROUTING,
DISTRIBUTION, and ACCOUNTING services and that they will continue to
provide these services to existing customers as well as offering them
to other CNs.
In this scenario, these CNs would interconnect with others via a CIG
that provides a REQUEST-ROUTING INTERNETWORKING SYSTEM, a
DISTRIBUTION INTERNETWORKING SYSTEM, and an ACCOUNTING
INTERNETWORKING SYSTEM. The net result of this interconnection would
be that a larger set of SURROGATES will now be available to the
CLIENTS.
Figure 1 shows three CNs which have interconnected to provide greater
scale and reach to their existing customers. They are all
participating in DISTRIBUTION INTERNETWORKING, REQUEST-ROUTING
INTERNETWORKING, and ACCOUNTING INTERNETWORKING.
As a result of the NEGOTIATED RELATIONSHIPS it is assumed that:
1. CONTENT that has been INJECTED into any one of these ORIGINATING
CNs may be distributed into any other ENLISTED CN.
2. Commands affecting the DISTRIBUTION of CONTENT may be issued
within the ORIGINATING CN, or may also be issued within the
ENLISTED CN. The latter case allows local decisions to be made
about DISTRIBUTION within the ENLISTED CN, but such commands would
not control DISTRIBUTION within the ORIGINATING CN.
3. ACCOUNTING information regarding CLIENT access and/or DISTRIBUTION
actions will be made available to the ORIGINATING CN by the
ENLISTED CN.
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RFC 3570 CDI Scenarios July 2003
4. The ORIGINATING CN would provide this ACCOUNTING information to
the PUBLISHER based on existing Service Level Agreements (SLAs).
5. CONTENT REQUESTS by CLIENTS may be directed to SURROGATES within
any of the ENLISTED CNs.
The decision of where to direct an individual CONTENT REQUEST may be
dependent upon the DISTRIBUTION and REQUEST-ROUTING policies
associated with the CONTENT being requested as well as the specific
algorithms and methods used for directing these requests. For
example, a REQUEST-ROUTING policy for a piece of CONTENT may indicate
multiple versions exist based on the spoken language of a CLIENT.
Therefore, the REQUEST-ROUTING SYSTEM of an ENLISTED CN would likely
direct a CONTENT REQUEST to a SURROGATE known to be holding a version
of CONTENT of a language that matches that of a CLIENT.
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RFC 3570 CDI Scenarios July 20034.2. BCN providing ACCOUNTING INTERNETWORKING and REQUEST-ROUTING INTERNETWORKING
This scenario describes the case where a single entity (BCN A)
performs ACCOUNTING INTERNETWORKING and REQUEST-ROUTING
INTERNETWORKING functions, but has no inherent DISTRIBUTION or
DELIVERY capabilities. A potential configuration which illustrates
this concept is given in Figure 2.
In the scenario shown in Figure 2, BCN A is responsible for
collecting ACCOUNTING information from multiple CONTENT NETWORKS (CN
A and CN B) to provide a clearinghouse/settlement function, as well
as providing a REQUEST-ROUTING service for CN A and CN B.
In this scenario, CONTENT is injected into either CN A or CN B and
its DISTRIBUTION between these CNs is controlled via the DISTRIBUTION
INTERNETWORKING SYSTEMS within the CIGs. The REQUEST-ROUTING SYSTEM
provided by BCN A is informed of the ability to serve a piece of
CONTENT from a particular CONTENT NETWORK by the REQUEST-ROUTING
SYSTEMS within the interconnected CIGs.
BCN A collects statistics and usage information via the ACCOUNTING
INTERNETWORKING SYSTEM and disseminates that information to CN A and
CN B as appropriate.
As illustrated in Figure 2, there are separate REQUEST-ROUTING
SYSTEMS employed within CN A and CN B. If the REQUEST-ROUTING SYSTEM
provided by BCN A is the AUTHORITATIVE REQUEST-ROUTING SYSTEM for a
given piece of CONTENT this is not a problem. However, each
individual CN may also provide the AUTHORITATIVE REQUEST-ROUTING
SYSTEM for some portion of its PUBLISHER customers. In this case
care must be taken to ensure that the there is one and only one
AUTHORITATIVE REQUEST-ROUTING SYSTEM identified for each given
CONTENT object.
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RFC 3570 CDI Scenarios July 20034.4. PCN ENLISTS multiple CNs
In the previously enumerated scenarios, PUBLISHERS have not been
discussed. Much of the time, it is assumed that the PUBLISHERS will
allow CNs to act on their behalf. For example, a PUBLISHER may
designate a particular CN to be the AUTHORITATIVE REQUEST-ROUTING
SYSTEM for its CONTENT. Similarly, a PUBLISHER may rely on a
particular CN to aggregate all its ACCOUNTING data, even though that
data may originate at SURROGATES in multiple distant CNs. Finally, a
PUBLISHER may INJECT content only into a single CN and rely on that
CN to ENLIST other CNs to obtain scale and reach.
However, a PUBLISHER may wish to maintain more control and take on
the task of ENLISTING CNs itself, therefore acting as a PCN (Section2.1). This scenario, shown in Figure 4, describes the case where a
PCN wishes to directly enter into NEGOTIATED RELATIONSHIPS with
multiple CNs. In this scenario, the PCN would operate its own CIG
and enter into DISTRIBUTION INTERNETWORKING, ACCOUNTING
INTERNETWORKING, and REQUEST-ROUTING INTERNETWORKING relationships
with two or more CNs.
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RFC 3570 CDI Scenarios July 20035. Security Considerations
Security concerns with respect to Content Internetworking can be
generally categorized into trust within the system and protection of
the system from threats. The trust model utilized with Content
Internetworking is predicated largely on transitive trust between the
ORIGIN, REQUEST-ROUTING INTERNETWORKING SYSTEM, DISTRIBUTION
INTERNETWORKING SYSTEM, ACCOUNTING INTERNETWORING SYSTEM, and
SURROGATES. Network elements within the Content Internetworking
system are considered to be "insiders" and therefore trusted.
5.1. Threats to Content Internetworking
The following sections document key threats to CLIENTs, PUBLISHERs,
and CNs. The threats are classified according to the party that they
most directly harm, but, of course, a threat to any party is
ultimately a threat to all. (For example, having a credit card
number stolen may most directly affect a CLIENT; however, the
resulting dissatisfaction and publicity will almost certainly cause
some harm to the PUBLISHER and CN, even if the harm is only to those
organizations' reputations.)
5.1.1. Threats to the CLIENT5.1.1.1. Defeat of CLIENT's Security Settings
Because the SURROGATE's location may differ from that of the ORIGIN,
the use of a SURROGATE may inadvertently or maliciously defeat any
location-based security settings employed by the CLIENT. And since
the SURROGATE's location is generally transparent to the CLIENT, the
CLIENT may be unaware that its protections are no longer in force.
For example, a CN may relocate CONTENT from a Internet Explorer
user's "Internet Web Content Zone" to that user's "Local Intranet Web
Content Zone". If the relocation is visible to the Internet Explorer
browser but otherwise invisible to the user, the browser may be
employing less stringent security protections than the user is
expecting for that CONTENT. (Note that this threat differs, at least
in degree, from the substitution of security parameters threat below,
as Web Content Zones can control whether or not, for example, the
browser executes unsigned active content.)
5.1.1.2. Delivery of Bad Accounting Information
In the case of CONTENT with value, CLIENTs may be inappropriately
charged for viewing content that they did not successfully access.
Conversely, some PUBLISHERs may reward CLIENTs for viewing certain
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RFC 3570 CDI Scenarios July 2003
CONTENT (e.g., programs that "pay" users to surf the Web). Should a
CN fail to deliver appropriate accounting information, the CLIENT may
not receive appropriate credit for viewing the required CONTENT.
5.1.1.3. Delivery of Bad CONTENT
A CN that does not deliver the appropriate CONTENT may provide the
user misleading information (either maliciously or inadvertently).
This threat can be manifested as a failure of either the DISTRIBUTION
SYSTEM (inappropriate content delivered to appropriate SURROGATEs) or
REQUEST-ROUTING SYSTEM (request routing to inappropriate SURROGATEs,
even though they may have appropriate CONTENT), or both. A REQUEST-
ROUTING SYSTEM may also fail by forwarding the CLIENT request when no
forwarding is appropriate, or by failing to forward the CLIENT
request when forwarding is appropriate.
5.1.1.4. Denial of Service
A CN that does not forward the CLIENT appropriately may deny the
CLIENT access to CONTENT.
5.1.1.5. Exposure of Private Information
CNs may inadvertently or maliciously expose private information
(passwords, buying patterns, page views, credit card numbers) as it
transmits from SURROGATEs to ORIGINs and/or PUBLISHERs.
5.1.1.6. Substitution of Security Parameters
If a SURROGATE does not duplicate completely the security facilities
of the ORIGIN (e.g., encryption algorithms, key lengths, certificate
authorities) CONTENT delivered through the SURROGATE may be less
secure than the CLIENT expects.
5.1.1.7. Substitution of Security Policies
If a SURROGATE does not employ the same security policies and
procedures as the ORIGIN, the CLIENT's private information may be
treated with less care than the CLIENT expects. For example, the
operator of a SURROGATE may not have as rigorous protection for the
CLIENT's password as does the operator of the ORIGIN server. This
threat may also manifest itself if the legal jurisdiction of the
SURROGATE differs from that of the ORIGIN, should, for example, legal
differences between the jurisdictions require or permit different
treatment of the CLIENT's private information.
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RFC 3570 CDI Scenarios July 20035.1.2. Threats to the PUBLISHER5.1.2.1. Delivery of Bad Accounting Information
If a CN does not deliver accurate accounting information, the
PUBLISHER may be unable to charge CLIENTs for accessing CONTENT or it
may reward CLIENTs inappropriately. Inaccurate accounting
information may also cause a PUBLISHER to pay for services (e.g.,
content distribution) that were not actually rendered. Invalid
accounting information may also effect PUBLISHERs indirectly by, for
example, undercounting the number of site visitors (and, thus,
reducing the PUBLISHER's advertising revenue).
5.1.2.2. Denial of Service
A CN that does not distribute CONTENT appropriately may deny CLIENTs
access to CONTENT.
5.1.2.3. Substitution of Security Parameters
If a SURROGATE does not duplicate completely the security services of
the ORIGIN (e.g., encryption algorithms, key lengths, certificate
authorities, client authentication) CONTENT stored on the SURROGATE
may be less secure than the PUBLISHER prefers.
5.1.2.4. Substitution of Security Policies
If a SURROGATE does not employ the same security policies and
procedures as the ORIGIN, the CONTENT may be treated with less care
than the PUBLISHER expects. This threat may also manifest itself if
the legal jurisdiction of the SURROGATE differs from that of the
ORIGIN, should, for example, legal differences between the
jurisdictions require or permit different treatment of the CONTENT.
5.1.3. Threats to a CN5.1.3.1. Bad Accounting Information
If a CN is unable to collect or receive accurate accounting
information, it may be unable to collect compensation for its
services from PUBLISHERs.
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RFC 3570 CDI Scenarios July 20035.1.3.2. Denial of Service
Misuse of a CN may make that CN's facilities unavailable, or
available only at reduced functionality, to legitimate customers or
the CN provider itself. Denial of service attacks can be targeted at
a CN's ACCOUNTING SYSTEM, DISTRIBUTION SYSTEM, or REQUEST-ROUTING
SYSTEM.
5.1.3.3. Transitive Threats
To the extent that a CN acts as either a CLIENT or a PUBLISHER (such
as, for example, in transitive implementations) such a CN may be
exposed to any or all of the threats described above for both roles.
6. Acknowledgements
The authors acknowledge the contributions and comments of Fred
Douglis (AT&T), Raj Nair (Cisco), Gary Tomlinson (CacheFlow), John
Scharber (CacheFlow), Nalin Mistry (Nortel), Steve Rudkin (BT),
Christian Hoertnagl (IBM), Christian Langkamp (Oxford University),
and Don Estberg (Activate).
7. References
[1] Day, M., Cain, B., Tomlinson, G. and P. Rzewski, "A Model for
Content Internetworking (CDI)", RFC 3466, February 2003.
[2] Biliris, A., Cranor, C., Douglis, F., Rabinovich, M., Sibal, S.,
Spatscheck, O. and W. Sturm, "CDN Brokering", Proceedings of the
6th International Workshop on Web Caching and Content
Distribution, Boston, MA, June 2001.
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RFC 3570 CDI Scenarios July 20039. Full Copyright Statement
Copyright (C) The Internet Society (2003). All Rights Reserved.
This document and translations of it may be copied and furnished to
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or assist in its implementation may be prepared, copied, published
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the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
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The limited permissions granted above are perpetual and will not be
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HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
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